The present invention is directed to mobile robots and more specifically to systems therefore which prevent mobile robots from being immobilized by or venturing past given obstructions.
Mobile robots have many applications in the home and industry. By mobile it is meant that the robot may move from one location to another. Upon or by moving between locations, the robot may transmit signals, such as sound, infra-red reception, video images, bomb detection, etc. to a remote location. A human operator may be disposed at the remote location, or the signal may be stored for subsequent retrieval. The mobile robot may patrol a given area for intruder detection or may clean a specific surface area, such as a carpet or a hard surface floor.
Carpeting and rugs are inclusive of woven and other fabric sheet goods intended for flooring without regard to pile or loop. Hard surface floors include, but are not limited to, hardwood, concrete, ceramic tile, vinyl, synthetic composition tile, linoleum, and smooth mats and laminates.
In the home, office and elsewhere hard surface floors are frequently adjacent to carpeted areas. Furthermore, homes often have hard surface floors with throw rugs thereon. A hard surface floor care robot mobilely performs maintenance and cleaning of such a floor, including mopping, polishing, dusting, waxing, etc. Such a robot should not go onto carpeted surfaces or the throw rugs while applying cleaning fluids, polish, oiled dusting cloths, wax etc. intended for the hard surface, otherwise damage to the carpet or throw rug may result. Conversely, cleaning solutions intended to be applied to carpeting or a rug may damage a hard surface floor. Traditional barriers such as walls and doors can not be depended upon to prevent hard surface care robots from moving onto a carpet or throw rug or vice versa.
Furthermore, a robot may be immobilized by a carpet or throw rug. The wheels and traction of a robot designed for mobility on a hard surface may be insufficient to propel the same robot across a carpet or throw rug. Furthermore, the robot may become trapped by the carpet, or more likely the throw rug, if the leading edge of the robot should move underneath and lift the carpet or throw rug.
Carpeting, throw rugs, and other barriers which may immobilize the robot or be damaged by the robot while it is in use are collectively referred to hereinafter as obstructions. An obstruction is a any obstruction in the path of the robot which may immobilize the robot, unduly restrict its movement, or be damaged by the robot performing its intended task.
U.S. Pat. No. 4,977,639 (Takahashi et al.) discloses a contact carpet sensor used in a manual vacuum cleaner to stop the brush from rotating on hard surface floors. The sensor consists, in part, of a narrow contact element which sinks into carpet but is supported on hard surface floors relative to a broader contact element. The ""639 patent teaches that the carpet is sensed only after the vacuum cleaner crosses the transition from hard surface to carpet or vice versa. The ""639 patent relies on carpet being substantially more penetrable than a hard surface, which may not be the case with tightly woven rugs. Further, this teaching provides no suggestion of how to avoid obstructions such as throw rugs which may immobilize the robot.
U.S. Pat. No. 5,144,715 (Matsuyo et al.) discloses vacuum cleaner dust pick-up dynamics used to determine floor type. Dust is removed from hard surface floors suddenly upon the application of the air flow while dust more gradually is vacuumed from carpet. This difference in air flow is detected with optical sensors. The ""715 patent is directed specifically to vacuum cleaners and the sensor reports a transition only after it has crossed a transition in the floor type.
U.S. Pat. No. 5,277,839 (Shultz et al.) discloses a permanent fluorescent dye material for establishing a guide path on the carpet for an automatic guided vehicle. The dye material fluoresces when exposed to ultraviolet light but is otherwise invisible. Lines drawn with the dye on carpet can be used to optically guide a vehicle. U.S. Pat. No. 4,707,297 discloses a similar scheme using a removable (washable) fluorescent dye.
U.S. Pat. No. 6,076,227 (Shallig et al) teaches a surface type detector for detecting a type of surface to be treated, which surface type detector comprises a vibration detector. An acoustic pulse is transmitted towards the floor. The amplitude of the reflection at various angles of incidence from the floor surface is used to determine the type of floor. Similar to the teachings cited above, the Shallig et al. sensor must travel over the transition between floor types before the transition is detected. Likewise, optical detectors of detecting carpet versus hard surface floor types rely on the relative reflectivity of the surfaces. Optical detectors cannot reliably distinguish between patterned/textured hard surfaces and carpet.
Consequently, a need still exists for a system which can assist a mobile robot in avoiding obstructions. Particularly, a need exists for a system by which a mobile robot can distinguish between hard surface floors and carpeting or rugs
The present invention comprises an obstruction management system for a mobile robot. The system comprises a plow. The plow is attached to the robot at a proximal end and extends outwardly therefrom to a distal end. The plow has a forward face disposed in acute angular relationship relative to the floor or other support surface upon which the robot sits. The plow is movable relative to another predetermined component of the robot. Suitable components include the chassis, suspension, etc. of the robot. Such relative movement is detectable by sensors.
Upon encountering an obstruction, the plow will either push it aside, raise it in elevation by having the distal end of the plow slide under the obstruction or the plow will move relative to the other component of the robot. Any of these three situations will obviate immobility of the robot due to the obstruction.
If the obstruction is pushed aside, it will not impede forward movement of the robot. If the plow slides under the obstruction, it will move upwardly, and likely become closer to the robot. As the obstruction moves upwardly, it will reach an elevation where it is detectable by sensors on the robot. Upon detection by the sensors, the robot will change its direction, avoiding the obstruction. If the obstruction causes the plow to move relative to the other predetermined component of the robot, such relative movement is detected by the sensors. Again, the robot will change its direction, avoiding the obstruction.
In another embodiment, drag on the robot wheels or other floor contacting surfaces may be monitored to detect any differential friction which occurs when the robot encounters a difference in surface type. Such detection may be accomplished by measuring current to the drive motors, or wheel revolutions versus power to the drive motors. In another embodiment, differences in floor type may be detected by measuring the position or displacement of a cleaning sheet biased against the floor.